Anatomical basis for apparent subepithelial cleft lip: a histological and ultrasonographic survey of the orbicularis oris muscle.

OBJECTIVE: To determine if there is an anatomic basis for subepithelial orbicularis oris muscle defects by directly comparing ultrasonographic images of the upper lip with corresponding histological sections obtained from cadavers.
METHODS: Ultrasound was performed on the upper lips of previously frozen, unpreserved cadaver heads (n = 32), followed by dissection and sectioning of the upper lips. The ultrasound sequences were scored by a panel of raters, classifying the orbicularis oris muscle as negative, positive, or unknown for the presence of an orbicularis oris discontinuity (subepithelial defect). Based on ultrasound, six lip specimens were chosen for histological sectioning, were stained with hematoxylin-eosin and Gomori trichrome stain, and were evaluated with light microscopy at low (8x) and intermediate (100x) magnification.
RESULTS: One cadaver was scored positive for an orbicularis oris muscle discontinuity based on ultrasound; whereas, the remaining cadavers were scored negative. Of the cadavers with negative ultrasound scores, two were noted to have orbicularis oris muscles with "irregular" features (e.g., excessive localized thinning or asymmetry). From histology, the area of discontinuity as visualized on the positively scored ultrasound was characterized by both disorganized orbicularis oris muscle fibers and excess connective tissue within the muscle belly. In contrast, the localized thinning observed on some of the negatively scored ultrasounds was not confirmed by histology.
CONCLUSIONS: Abnormalities of the orbicularis oris muscle visualized by ultrasound have an anatomic basis as revealed through histology. Ultrasound is a useful tool for noninvasively identifying discontinuities of the orbicularis oris muscle.